1. Field of the Invention
The present invention is directed to an x-ray diagnostics installation including a spatial frequency filter in the image processing system.
2. Description of the Prior Art
X-ray diagnostics installations are known which include an x-ray tube and an image pick-up and playback system which includes an image memory, a spatial frequency filter and a monitor. Such x-ray diagnostics installations achieve an intensification of the fine or detail contrast of x-ray images. A video system for use in such a system for x-ray fluoroscopy is disclosed in German Patent 1 224 352. In this known system, a video high-pass filter, which contains an image pick-up tube as a memory, is connected in the transmission channel. Large-area contrast regions are thereby attenuated, whereas the high-frequency signal components, which represent the detail contrasts, are amplified. The ongoing video signal is subtracted in two subsequent differential stages from the filtered signal and the difference signal respectively, and the degree of intensification is set by a controllable amplifier. An intensification of the detail contrasts in this known installation is not possible during the generation of fluoroscopic images because the quantum noise is amplified together with the useful signal, the detail contrast signal, so that it has a negative influence in the image observation, even though the signal-to-noise ratio is not changed. In this known device, therefore, in the fluoroscopic mode the spatial frequency filter, which is a spatial high-pass filter, is therefore partially disconnected, or set to operate only at a very weak level.
Another installation is described in German Patent 30 07 620 which, for fluoroscopy includes a motion detector which effects an increase in the dose rate and a reduction in the integration time dependent on the amount of motion.